Pressure ring for transformer windings

ABSTRACT

Pressure ring apparatus for securing the windings of power transformers. The pressure ring includes a body portion with magnetic radial members positioned therein to direct the leakage flux from the winding structure back into the magnetic core. The radial members are constructed from a plurality of metallic laminations which are stacked with their edges perpendicular to the leakage flux. Other magnetic members may be positioned in the body portion to help direct the leakage flux into the radial members. In one embodiment of this invention, one side of the pressure ring is stepped to conform to the shape of the yoke portion of the magnetic core.

United States Patent [1 1 Rissinger [45.1 July 31, 1973 1 PRESSURE RING FOR TRANSFORMER WINDINGS [7S] lnventor:

Nov. 30, 1971 John C. Rissinger, Sharon, Pa.

[22] Filed:

' 211 Appl. No.: 203,226

[52] U.S. Cl 336/84, 336/197, 336/212, 336/234 [51] Int. Cl. I-IOII 27/24 [58] Field of Search 336/84, 212, 214, 336/215, 234, 197

[56] References Cited UNITED STATES PATENTS 2,962,679 11/1960 Stratton ..336/212X 1,245,197 9/1971 Great Britain 336/234 1,401,109 4/1965 France 336/234 1,201,855 7/1959 France 336/215 Primary ExaminerThomas .l. Kozma Attorney-A. T. Stratton, F. E. Browder et al.

[57] ABSTRACT Pressure ring apparatus for securing the windings of power transformers. The pressure ring includes a body portion with magnetic radial members positioned therein to direct the leakage flux from the winding structure back into the magnetic core. The radial members are constructed from a plurality of metallic laminations which are stacked with their edges perpendicular to the leakage flux. Other magnetic members may be positioned in the body portion to help direct the leakage flux into the radial members. In one embodiment of this invention, one side of the pressure ring is stepped to conform to the shape of the yoke portion of the magnetic core.

5 Claims, 7 Drawing Figures PAIENIEUJm. 3 I ma SHEET 2 [IF 2 ll PRESSURE RING FOR TRANSFORMER WINDINGS BACKGROUND OF THE INVENTION 1. Field of The Invention This invention relates, in general, to electrical inductive apparatus and, more specifically, to pressure rings for power transformer windings.

2. Description of The Prior Art Pressure rings are used at the ends of the winding structures of power transformers to maintain the size and position of the winding structures when subject to high stress conditions. In power transformers having a relatively large amount of leakage flux, the pressure ring carries a substantial amount of flux when it is constructed from a magnetic material.

To reduce eddy currents in the pressiire ring and to improve the overall efficiency of the power transformer, laminated metallic pressure rings have been used. Such a pressure ring is described in U.S. Pat. No. 3,366,907, which is assigned to the same assignee as this invention. Although the type of pressure ring described in the referenced patent reduces eddy currents in the ring and reduces the heat generated therein, the leakage flux entering the ring does not find a low reluctance path back into the magnetic core. The laminations are arranged in such a manner that the flux must flow across the lamination faces to enter the magnetic core. Since this direction does not provide a low reluctance path for the flux, very little leakage flux is directed into the magnetic core and the efficiency of the transformer suffers.

Therefore, it is desirable, and it is an object of this invention, to provide a pressure ring constructed to furnish a relatively lower reluctance path for the leakage flux than prior art pressure rings so that the leakage flux may enter the magnetic core and improve the efficiency of the transformer.

SUMMARY OF THE INVENTION There is disclosed herein new and useful pressure rings for power transformers. The pressure rings may be constructed of a non-magnetic material which has magnetic radial members positioned therein to direct the leakage flux into the transformer core. The radial members are constructed of magnetic members, such as grain oriented magnetic steel strips, with the edges of the strips perpendicular to the longitudinal axis of the winding structure. Additional magnetic members may be positioned between the radial members to help bring the leakage flux into the radial members. The size and shape of the pressure ring depends upon the type and rating of the transformer and upon other factors. One portion of the pressure ring may be stepped to conform to the shape of the yoke portion of the magnetic core.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIG. I is a cutaway view ofa power transformer having pressure rings constructed according to the teachings of this invention;

FIG. 2 is a top view ofa pressure ring constructed according to the teachings of one embodiment of this invention;

FIG. 3 is a top view of a pressure ring constructed according to the teachings of another embodiment of this invention;

FIG. 4 is a top view of a pressure ring constructed according to the teachings of still another embodiment of this invention;

FIG. 5 is a partial elevational view of a transformer core of the flat-yoke type having installed thereon a pressure ring constructed according to the teachings of this invention;

FIG. 6 is a partial elevational view of a transformer core of the stepped-yoke type having installed thereon a pressure ring constructed according to the teachings of this invention; and

FIG. 7 is an isometric view of the pressure ring shown in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar members in all figures of the drawings.

Referring now to the drawings, and FIG. I in particular, there is shown a power transformer having a casing 110, a magnetic core 12, and longitudinal, hollow, winding structures M, 16 and 18. The casing 10 contains a fluid collant 20 and supports the high voltage bushings 22, 24 and 26 and the low voltage bushing 2%. Although they would normally be present, the lower structures of the bushings and the winding leads are not illustrated for clarity.

The top end frame 30 and the bottom end frame 32 support the magnetic core 12 and the winding structures I4, 16 and I8. Insulating material 34 is placed between each winding structure and the end frames. Pressure rings 36, 38 and 40 are illustrated adjacent to the top ends of the winding structures I4, 16 and 18, re spectively. Similar rings are located adjacent to the lower ends of each winding structure. The detailed construction of the pressure rings will be described hereinafter. The leakage flux existing near the ends of the winding structures enters the pressure rings and is directed back into the magnetic core l2.

FIG. 2 is a top view of a pressure ring constructed according to an embodiment of this invention and positioned around a leg 42 of a cruciform-type magnetic core. The pressure ring is substantially circumferential and includes a body portion 44 having a central opening 45 and a plurality of magnetic radial members 46 mounted in the body portion 44. The radial members 46 may comprise a plurality of metallic laminations dd which are placed in the body portion 44. The number of laminations per radial member 46, the number of radial members 46, and the average separation distance d between the radial members 46 is dependent upon the type and rating of the transformer.

Sufficient performance may be obtained with a pressure ring similar to the pressure ring 40 illustrated in FIG. 3. The body portion 50 of the pressure ring shown in FIG. 3 contains radial members 52 which have more laminations 54 per radial member than the arrangement shown in FIG. 2. The average separation distance D is greater than the arrangement shown in FIG. 2.

The pressure ring embodiments illustrated in FIGS. 2 and 3 operate in substantially the same manner. In general, the leakage flux at the end of the winding structures is oriented in an axial direction. This causes the flux to enter the edges of the laminations forming the radial members. The flux is carried in a radial direction into the core leg 42 where it may reinforce the flux already in the core to increase the coupling between the coils of the winding structure, thus increasing the efficiency of the transformer. This also prevents the leakage flux from entering the end frame and casing to generate undesired heat in the end frame and easing. Heat generated in the end frames and the casing constitutes a power loss and also causes rapid deterioration of the insulation. The leakage flux which leaves the windings at a location which is between the radial members, such as the region 51, has a tendency to bend over and enter the radial members. Therefore, with a sufficient number of radial members, the leakage flux is satisfactorily directed by the radial members into the core leg 42.

The pressure rings shown in FIGS. 2 and 3 may have magnetic members disposed in a circular arrangement between the radial members. FIG. 4 illustrates an embodiment of the pressure ring shown in-FIG. 3 wherein the magnetic members 56 are placed between the radial members 52. Each magnetic member 56 is constructed of a plurality of metallic laminations 58. The members 56 direct the flux into the radial members 52 where it is then directed into the magnetic core leg 42. The number of laminations 58, the size of the members 56, the radial location of the members 56, and other variables may be altered without departing from the teachings of this invention. The members 56 shown in FIG. 4 are radially positioned near the center of the pressure ring body portion 50 since a high concentration of leakage flux occurs in this region due to the separation of the high and low voltage windings of the winding structure.

FIG. 5 is a partial side elevational view illustrating a mounting arrangement of the pressure ring 40. In FIG. 5, the pressure ring 40 is mounted adjacent to the bottom end of the winding structure 62 with an insulating member 64 therebetween. The mounting arrangement for the upper pressure ring is substantially similar. Pressure producing means which forces the pressure rings against the winding structure 62 is not shown.

The pressure ring 40 is supported by the end frame members 32. The side 41 of the pressure ring 40 is substantially flat. The lower portion 42 is also substantially flat and rests on the flanges 33 and the top portion of the bottom magnetic core yoke. The laminations 66 are located in the pressure ring 40 with their edges perpendicular to the longitudinal axis of the winding structure 62. This permits each lamination 66 to receive leakage flux through its edge.

The pressure ring 68 illustrated in FIG. 6 is associated with a magnetic core having a yoke section with a stepped upper portion. That is, the yoke has a cruciformtype cross-section similar to the core legs. The winding structure 70 is separated from the pressure ring 68 by the insulating material 72. The pressure ring 68 rests on the flanges 74 of the end frame members 76 and also on the stepped portions of the magnetic core yoke.

With the arrangement shown in FIG. 6, the upper portion 78 of the pressure ring 68 is substantially flat and is located approximately even with the upper portion of the magnetic core yoke. The lower portion of the pressure ring 68 is stepped to permit its placement around the yoke with a sufficient area thereof resting on the yoke to provide adequate mechanical strength. In this embodiment, the pressure ring 68 does not be cupy any space between the top portion of the yoke and the winding structure. Additionally, the laminations may have a width dimension w equal to the stepped dimension s without requiring any extension of the pressure ring 68 above the upper portion of the yoke surface.

An isometric view of the pressure ring 68 is shown in FIG. 7. The upper portion 82 of the yoke is flush with the upper portion 78 of the pressure ring 68. The radlal members 84 are formed from a plurality of laminations 80. A radial member is not required over the yoke portion 82 since the yoke portion effectively catches the leakage flux at that location.

Although the pressure ring 68 is shown with a gap equal to the width of the upper yoke portion 82, the ring may be constructed without any gap if strength considerations require such. In such a case, the upper portion 78 of the pressure ring 68 would be above the upper portion 82 of the yoke.

The pressure ring 68, as well as the pressure rings in the other embodiments of this invention, may be constructed of a non-magnetic material. A suitable material would consist of a laminated fibrous material, such as wood, having an epoxide as a bonding material.

There has been disclosed new and useful pressure ring apparatus which directs the leakage flux into the transformer core. A model transformer was constructed and tested using different types of pressure rings. One transformer arrangement having pressure rings constructed according to the teachings disclosed in US. Pat. No. 3,366,907 had a 2,523 watt loss due to eddy currents in the windings, end frames and pressure rings at percent rated load. Another transformer arrangement having pressure rings constructed similar to the pressure ring illustrated in FIG. 6 of this patent application had a loss of only 1,895 watts for similar portions of the transformer at I00 percent rated load.

Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description or shown in the accompanying drawings, shall be interpreted as illustrative rather than limiting.

I claim as my invention:

1. A pressure ring for installation adjacent to an end of a transformer winding structure, comprising a nonmagnetic body portion having upper and lower surfaces, the lower surface of said body portion having steps therein which conform to the shape of the magnetic core of the transformer, and magnetic members all aligned generally in a radial direction through said body portion, said magnetic members being positioned in grooves formed in said non-magnetic body portion.

2. The pressure ring of claim 1 wherein the body portion is constructed of laminated fibrous material bonded together by an epoxide.

3. The pressure ring of claim 1 wherein the magnetic members are constructed of a plurality of laminated magnetic strips, said strips positioned with their edges perpendicular to the longitudinal axis of the winding structure.

4. The pressure ring of claim 1 wherein the body por tion also contains magnetic members all aligned generally in a circular direction around the longitudinal axis jacent to said yoke section of said core, said nonmagnetic body portion which forms said second side being stepped to conform to the shape of said yoke section, said radial members being constructed of a plurality of laminations of magnetic strips, said strips being positioned in a radial direction with their edges perpendicular to the longitudinal axis of the winding structure.

=l i W 0' 

1. A pressure ring for installation adjacent to an end of a transformer winding structure, comprising a non-magnetic body portion having upper and lower surfaces, the lower surface of said body portion having steps therein which conform to the shape of the magnetic core of the transformer, and magnetic members all aligned generally in a radial direction through said body portion, said magnetic members being positioned in grooves formed in said non-magnetic body portion.
 2. The pressure ring of claim 1 wherein the body portion is constructed of laminated fibrous material bonded together by an epoxide.
 3. The pressure ring of claim 1 wherein the magnetic members are constructed of a plurality of laminated magnetic strips, said strips positioned with their edges perpendicular to the longitudinal axis of the winding structure.
 4. The pressure ring of claim 1 wherein the body portion also contains magnetic members all aligned generally in a circular direction around the longitudinal axis of the winding structure and located between the radial magnetic members.
 5. A transformer comprising a magnetic core with a cruciform-type yoke section and a longitudinal winding structure with first and second ends, a pressure ring having first and second sides, said pressure ring comprising a non-magnetic body portion with radial members disposed in grooves therein, said first side being substantially flat, said second side being positioned adjacent to said yoke section of said core, said non-magnetic body portion which forms said second side being stepped to conform to the shape of said yoke section, said radial members being constructed of a plurality of laminations of magnetic strips, said strips being positioned in a radial direction with their edges perpendicular to the longitudinal axis of the winding structure. 